1. Field of the Invention
The present invention relates to a focus test mask formed with a pattern for measuring focus information (image plane information) of a projection optical system, a focus measuring method for measuring the focus information of the projection optical system by using the focus test mask, an exposure method, an exposure apparatus provided with the focus test mask, and a method for producing a device using the exposure apparatus.
2. Description of the Related Art
For example, the following procedure is performed in order to measure the focus information as the information about an image plane (best focus position) of a projection optical system in relation to an exposure apparatus used in the lithography step to produce an electronic device (microdevice) such as a semiconductor device or the like. That is, a test mask is arranged on an object plane of the projection optical system, and a substrate or the like is arranged on the image plane of the projection optical system. A predetermined evaluating pattern, which is provided on the test mask, is projected onto the substrate or the like via the projection optical system to measure, for example, a positional deviation amount or positional shift amount of an image of the evaluating pattern.
A method is known as a first conventional measuring method, wherein an evaluating pattern, which is provided with a phase changing portion for changing the phase of an illumination light (illumination light beam) at a space portion wider than the line width of each of line patterns between the line patterns each constructed of two light shielding films, is used, and a substrate coated with a photoresist is exposed with an image of the evaluating pattern formed by a projection optical system. See, for example, Japanese Patent Application Laid-open No. 6-204305. In this procedure, it is possible to determine the defocus amount of the surface of the substrate as well as the position of the image plane from the spacing distance between two line-shaped resist patterns formed on the substrate after the development.
A method is known as a second conventional measuring method, wherein a wafer is exposed in an overlay manner with an image of a diffraction grating-shaped evaluating pattern which includes a plurality of, for example, four or more light shielding lines such that phase distributions provided outside the respective light shielding lines are asymmetrical in the measuring direction and an image of a trim pattern, which is provided to extinguish or erase any image of any unnecessary light shielding line disposed on an outer side, of images of the plurality of light shielding lines. See, for example, Japanese Patent No. 3297423. Also in this case, it is possible to determine the defocus amount of the surface of the wafer from the shift amounts of the images of the plurality of remaining light shielding lines disposed at the center.
A method is known as a third conventional measuring method, wherein the lateral deviation amount is measured for a spatial image of an evaluating pattern which is provided in the vicinity of a plurality of line patterns and which has a phase shift portion wider than the line width of each of the line patterns. See, for example, International Publication No. 2005/004211. Also in this case, it is possible to determine the defocus amount of the light-receiving surface from the lateral deviation amount of images of the respective line patterns.
In the first and third measuring methods of the conventional measuring methods for measuring the focus information, the phase shift portion, which is disposed in contact with the line pattern (or in the vicinity thereof), has a width which is wider than the line width of the line pattern. In order to enhance the measuring sensitivity (lateral deviation amount of image/defocus amount), it is preferable that the line width of the line pattern is narrowed. However, if the line width of the line pattern is narrowed, it is feared that the reproducibility of measurement (measuring reproducibility) might be lowered. Further, in a case that the image of the resist pattern after the development is observed, it is feared that the falling (collapse) or the like of the resist pattern might be caused. Further, if the line width of the line pattern is narrow as described above, in a case that the numerical aperture of the projection optical system is high or large, it is feared that the measuring sensitivity might be lowered especially in a range in which a projection surface of the image of the line pattern is disposed near to the best focus position.
On the other hand, the second conventional measuring method involves such a problem that the efficiency of measurement (measuring efficiency) is low, because it is necessary to perform the exposure twice in order to extinguish the image of the unnecessary pattern.